linux-kernel - Re: [PATCH v3 1/1] ppc/crash: Reset spinlocks during crash

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Message-ID: <87mu6dbfjm.fsf@mpe.ellerman.id.au>
Date:   Tue, 12 May 2020 20:42:21 +1000
From:   Michael Ellerman <mpe@...erman.id.au>
To:     Paul Mackerras <paulus@...abs.org>
Cc:     Leonardo Bras <leonardo@...ux.ibm.com>,
        Nicholas Piggin <npiggin@...il.com>,
        Alexios Zavras <alexios.zavras@...el.com>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Christophe Leroy <christophe.leroy@....fr>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Enrico Weigelt <info@...ux.net>, peterz@...radead.org,
        Thomas Gleixner <tglx@...utronix.de>,
        linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org
Subject: Re: [PATCH v3 1/1] ppc/crash: Reset spinlocks during crash

Paul Mackerras <paulus@...abs.org> writes:
> On Wed, Apr 08, 2020 at 10:21:29PM +1000, Michael Ellerman wrote:
>> 
>> We should be able to just allocate the rtas_args on the stack, it's only
>> ~80 odd bytes. And then we can use rtas_call_unlocked() which doesn't
>> take the global lock.
>
> Do we instantiate a 64-bit RTAS these days, or is it still 32-bit?

No, yes.

> In the old days we had to make sure the RTAS argument buffer was
> below the 4GB point.

Yes you're right, that's still true.

I was thinking we were on the emergency stack, but we may not be.

> If that's still necessary then perhaps putting rtas_args inside the
> PACA would be the way to go.

Yeah I guess. Allocating a struct within the RMO for each CPU is not
that simple vs just putting it in the paca.

cheers